The objectives of these studies are to characterize the interrelationship between vasomotor activity, vascular injury and thrombosis in the epicardial coronary arteries. Studies will be performed in chronically instrumented dogs using ultrasonic dimension crystals to monitor vasomotor activity. The following specific hypotheses will be studied. 1. Endogenous and exongenous adrenergic stimulation effects, Alpha adrenergic constriction and Beta adrenergic relaxation in epicardial coronary arteries in the conscious dog; the predominant effect in the normal coronary artery is Beta adrenergic relaxation. 2. Endogenous and exogenous vasoactive compounds effect significant vasoconstriction/vasodilation of normal epicardial arteries in the conscious dog. 3. The normal endothelium modulates basal vasomotor activity and the responses to endogenous and exogenous adrenergic stimulation and endogenous and exogenous vasoactive compounds; endothelial denudation will alter basal vasomotor activity and certain of these responses. 4. Localized endothelial injury and progressive thrombosis releases vasoactive compounds that produce local and regional vasoconstriction of the epicardial and intramural vasculature. 5. Local endothelial injury and progressive thrombosis alters the response to endogenous and exogenous adrenergic stimulation and the response to endogenous and exogenous vasoactive compounds. 6. Coronary vasoconstriction in the presence of partial vessel occlusion effects platelet aggregation and progressive thrombosis. These studies address questions that are fundamental to the understanding of the clinical syndrome of coronary artery spasm and thrombosis and myocardial ischemia and infarction.